Gear Pump is one type of positive displacement rotary pump. In a gear pump, a fluid moves by enclosing a fixed volume of fluid using the interlocking gears and then transferring it as the gear rotates.
This pump delivers a pulse-free flow that is directly proportional to the rotational speed of the gears.
The gear pump is mainly used for developing high pressure.
The gear pump is a positive displacement pump and is also a fixed displacement pump.
Positive displacement Pump means that this pump provides a constant flow at a fixed speed regardless of the change in pressure and a fixed displacement pump means that it ejects a fixed quantity of fluid per revolution of the shaft.
The gear pump was invented by Johannes Kepler around 1600.
In a gear pump, there are generally two gears. One gear is the driver gear or the power gear and the other one is driven or the idle gear. The driver gear is connected to some prime movers or any mechanical energy source.
The driver gear is also known as master gear and the driven gear is also known as slave gear.
The driver gear is either rotated by using an electric motor or by using an IC Engine or by using a hand.
Components Of a Gear Pump:
1) Driver Gear:
Driver Gear is connected to the prime mover. It rotates using the power from the prime mover.
2) Driven Gear Or Idle Gear:
The driven gear is in mesh with the drive gear and rotates as the driver gear rotates.
Both the driver gear and the driven gear are packed inside the casing of the gear pump.
3) Inlet Section Or Suction Side:
It is the section in the gear pump through which fluid enters the gear pump. Low-pressure liquid enters the pump from the Inlet Section.
4) Outlet Section Or Discharge Side:
It is the section in the gear pump through which pressurized fluid is delivered to the required area. High-pressure liquid flows out from the pump from the Outlet Section.
5) Prime Mover:
In the gear pump, the prime mover is used to provide power to the shaft in which the driver gear is mounted. It can be an Electric Motor or an I.C Engine or it can be manual labour.
6) Safety Valve or Release Valve:
A safety valve or release valve is installed on the discharge side so that if excess pressure is generated,it can be released the pump can be prevented from getting damaged.
Working Of Gear Pump:
At starting the gear pump is started by providing power to the driving shaft and the driving gear starts to rotate using the power from the prime mover.
The driven gear which is in mesh with the driver gear also rotates as the driver gear rotates but in opposite direction.
As both the gears start rotating a partial vacuum is created on the suction side.
As the vacuum is created, the liquid in the suction side gets sucked towards the gear.
After that, the sucked liquid gets trapped between the gear and the casing.
Then the trapped liquid between the casing and the gear teeth travels along with the rotation of gear teeth and moves from the suction side towards the discharge side.
Similarly, the liquid flow from the suction side to the discharge side in the idle gear also and high-pressure liquid leaves the pump from the discharge side.
The liquid from the suction side cannot move directly to the discharge side and also from the suction side to the discharge side because the two gears are completely engaged and there is no gap for the liquid to flow.
Types Of Gear Pump:
Generally, gear pumps are of five types:
1) External Gear Pump
2) Internal Gear Pump
3) Lobe Pump
4) Ge-rotor Pump ( Generated Rotor Pump )
5) Screw Pump
1) External Gear Pump:
>> In an external gear pump, external gears are used to pump fluid.
In the external gear pump, two helical or spur gear are meshed with each other and mounted inside the casing.
>> The gears used in this type of pump are external meshing types. Any gear type either helical gear or spur gear or any other type of gear can be used in this type of pump.
>> Of the two gears, one is the driver gear and the other is the driven gear.
>> In the external pump, a partial vacuum is created at the inlet of the pump.
2) Internal Gear Pump:
>> In an internal gear pump, the gears used to pump fluid has internal meshing.
>> In the internal gear pump, the inner gear is the smaller one and has external teeth and the outer gear is the bigger gear and has internal teeth.
>> Between the two gears of the internal gear pump a crescent seal is provided which fills the gap between the two gears.
>> As the teeth of the inner gear come out of mesh with the outer gear, a partial vacuum is created due to which the fluid enters the gap between the crescent seal and the inner gear. After that, the fluid is trapped between the inner gear and crescent seal and travels from the inlet to the outlet of the internal gear pump.
3) Lobe Pump:
>> It is another type of external gear pump.
>> In lobe pump, vanes are used in place of gear teeth. The number of lobes can 3 or 4 depending on the requirements.
>> The two lobes are fitted inside the casing.
>> The lobes are designed in such a way that the lobes almost each other rather than just touch and rotate like in the case of the external gear pump.
>> Due to large size vanes and less number of vanes, higher discharge is achievable.
4) Ge- Rotor (Generated Rotor) Pump:
>> This pump has two generated rotors.
>> One rotor has external teeth and the other has internal teeth.
>> The rotor with external teeth rotates inside the rotor with internal teeth.
>> The number of teeth of the inner rotor is one less than that of the outer rotor.
>> The shaft of the prime mover is coupled with the inner rotor. Hence, the inner rotor is called the driver rotor.
>> Near the top of the Ge-rotor pump the pocket size i.e the space between the outer and inner rotor is negligible. This pocket-size keeps on increasing in the subsequent outer rotor teeth up to 180 degrees. So, the fluid is sucked near the inlet due to the vacuum between the inner rotor teeth and outer rotor teeth.
After 180 degrees when the fluid reaches the bottom part of Ge-rotor pump the pocket size starts decreasing causing the fluid the get delivered through the outlet.
5) Screw Pump:
>> It is named screw pump because the screw is used in this pump to increase the pressure of the fluid.
>> In this pump the inlet is divided into two parts and it has one outlet.
>> In the screw pump, one shaft has a left-hand screw and another shaft has a right-hand screw.
>> The two inlets are present at the ends and the outlet is in the middle on the opposite side.
>> When the pump is started, the liquid fills the gap between the threads of the screw at the inlet side, and this liquid moves axially along the screws from inlet to outlet due to rotation of the screws.
Advantages Of Gear Pump:
1) These pumps are very simple and compact with very few numbers of moving parts.
2) The maintenance cost of this type of pump is very low.
3) It has a low cost.
4) Gear pump can be used for generating very high pressure up to 3000 psi.
5) It can be used to pump highly viscous fluids like oils which cannot be pumped using centrifugal pumps.
There are very low chances of leakage while pumping high viscous liquid like oil in the gear pump. Hence, the efficiency of this pump increases when pumping highly viscous liquids.
6) Gear pumps can run in both directions. Hence, a single pump can be used for both loading and unloading purposes.
7) This pump is very less sensitive to contamination.
Disadvantages Of Gear Pump:
1) As meshing gears are used, abrasive fluids cannot be used in the gear pump.
2) These pumps are very noisy.
3) The size of gear pumps is limited so it can not be used for large bulk flow rates.